The scientific and practical importance of the research work can hardly be overestimated where the studies concern the mechanism of movement under gravity of bulk materials (fuels) because the physical-and-mechanical properties and flow regularities thereof are exceedingly important for design of fuel bins and batch feeders.
The manufacturing procedure and constructional features of the bin cannot be chosen correctly unless the regularities of motion of fuel having a complicated grain-size composition and moisture content are studied in detail.
Mechanics of bulk materials are absolutely indispensable in solving many problems relating to flow of fuel from the bin.
The physical-and-mechanical properties of bulk materials and the laws of motion and flow thereof have been widely studied both at home and abroad.
All the studies carried out in the Soviet Union and elsewhere and dealing with mechanics of free-flowing bulk media define the basic parameters characterizing the physical state of bulk materials and propose various methods for determination of minimum size of the bin outlet holes depending on the incline of the outlet funnel walls, and to the normal and tangential stresses occuring in bulk materials.
They also treat the problems of bridging peculiar to bulk materials (fuels) and consider the provisions for even and continuous flow thereof.
There are also proposed preferable design options depending on the physical-and-mechanical properties of materials being handled.
Various types of unloading facilities and feeders, such as those adapted to stimulate the flow of material (fuel) through the outlet hole are considered.
The flow of bulk materials (fuels) out of the bin is commonly intermittent. This occurs due to repeated sticking of fuel in the outlet hole, adherence of large quantities of fuel to the walls, formation of stable arched cavities, etc.
In most cases the above-mentioned disadvantages are corrected manually by means of pokers. This laborous procedure is intended to preclude reduction of the number of the operating fuel mills which would otherwise disturb the fuel burning conditions and lead to high heat losses chiefly because mechanical combustion is not complete.
Hence, the efficiency of the boiler installation drops and the fuel consumption rises.
Yet, the measures against bridging and sticking do not in all cases bring about the desirable effects, and are sometimes even detrimental.
Large-scale observations at electric power plants and detailed analysis of the Soviet and foreign sources dealing with operation of the bins show that the foregoing disadvantages can be overcome by increasing the outlet hole area and bin wall incline, and by stirring fuel near the outlet hole.
The above-mentioned measures taken separately do not provide for failure-free operation of the bin, especially when the flow properties of fuel are poor.
It is therefore expedient that the measures taken to ensure continuous supply of fuel be combined.
The feeders known in the art fail to meet the requirements to efficient and continuous delivery of high-moisture ordinary fuels.
The prior-art combination feeders are essentially aggregates consisting of a drum batcher with receiver and outlet tubes, and a band conveyor, and are applicable for handling high-grade low-moisture sized fuels free from clay inclusions. If the receiver tube cross-section area is small, malfunctions occur due to bridging of fuel inside the bin, and the batcher and the conveyor are clogged even through the fuel moisture content is medium. When said feeders are used for handling dry fuel, some of it inadvertently by-passes the batcher. Besides, the feeders are quite easily clogged with foreign objects.
The above disadvantages lead to low operating dependability of the feeder as a whole.
In order to improve the operating dependability, some foreign-made scraper feeders employ gates comprising sections that open alternately in predetermined succession.
A disadvantage inherent of this type of the feeders resides in that they use divider partitions between the gates which have turned to promote the bridging effects. In addition, said feeders do not alter the tubular shape of fuel flow at the bin outlet with the result that the efficiency and continuity of fuel supply are impaired.
Also known in the art are feeders of bulk materials (fuels) adapted for delivery of high-moisture unsized clayish ordinary fuels tending to stick and bridge, wherein fuel is supplied from the bin to the mill in the fuel pulverizing systems of thermal electric power plant boiler installations operating either under vacuum or pressure, with each feeder comprising a batcher, the case whereof is separated into two sections, with bands in each individual section moving in the same direction and with the bands in different sections moving in opposite directions, wherein a top part of the batcher case incorporates a receiver tube for receiving bulk materials (fuels), and a bottom part of the batcher case incorporates an outlet tube wherethrough the bulk material (fuel) is delivered from the batcher to a feeder conveyor (cf. USSR Inventor's Certificate No. 334,902, Cl. B65G, dated Apr. 19, 1971 and USSR Inventor's Certificate No. 278,000, Cl. 23C, dated Feb. 6, 1968).
However, the foregoing feeder, just like the other analogs, does not permit, simplification of manufacture of the feeder, substantial reduction of consumed metal and even fuel supply because of sticking of lumps in fuel containing clay admixtures, and does not provide for balanced loading of the boiler installation and for appropriate maintenance and repair conditions.
In addition, when one section of the feeder fails, the load drops by half, i.e. by 50 percent, with the band speed and fuel layer thickness remaining the same.